Micro-machined filter for magnetic particles

ABSTRACT

A method for filtering magnetic particles includes spinning a filter including a plurality of pores within a substrate. The method further includes applying, subsequent to spinning the filter, an external magnetic field to the filter. The method includes disposing a solution including a first particle and a second particle onto the filter. The first particle includes a magnetic particle of interest. The method further includes separating the first particle from the second particle by capturing the first particle within a pore of the plurality of pores within the substrate.

BACKGROUND

The present invention generally relates to fabrication methods andresulting structures for particle filters. More specifically, thepresent invention relates to micro-machined filters for magneticparticles.

Filtration devices are used in a variety of fields, includingpharmaceutical technology, biotechnology, bio-separation (e.g., plasmafractionation), and diagnostics. For many applications within theseareas, desirable features for such filtration devices include precisecontrol of pore sizes and distributions, absolute pore sizes as small asthe nanometer (nm) range, mechanical strength, high throughput, and highdurability.

SUMMARY

Embodiments of the present invention are directed to a method forfiltering magnetic particles. A non-limiting example of the methodincludes spinning a filter including a plurality of pores within asubstrate. The method further includes applying, subsequent to spinningthe filter, an external magnetic field to the filter. The methodincludes disposing a solution including a first particle and a secondparticle onto the filter. The first particle includes a magneticparticle of interest. The method further includes separating the firstparticle from the second particle by capturing the first particle withina pore of the plurality of pores within the substrate.

Embodiments of the present invention are directed to a filter system forfiltering magnetic particles. A non-limiting example of the filtersystem includes a micro-machined filter including a plurality of poreswithin a substrate. The filter system further includes a chamberincluding a surface for spinning the filter. The filter system includesa magnetic field generating device for applying a magnetic field to thefilter.

Embodiments of the present invention are directed to a micro-machinedfilter for filtering magnetic particles. A non-limiting example of themicro-machined filter includes a plurality of pores within a substrate.The micro-machined filter further includes a magnetic liner arranged onsidewalls of pores of the plurality of pores. A pore of the plurality ofpores has a width that is greater than a magnetic particle of interest,such that the magnetic particle of interest binds to the magnetic linerwithin the pore.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1A depicts a top view of a filter according to embodiments of thepresent invention;

FIG. 1B depicts a cross-sectional side view of the filter shown in FIG.1A;

FIG. 2 depicts a cross-sectional side view after spinning the filtershown in FIG. 1B according to embodiments of the present invention;

FIG. 3 depicts a cross-sectional side view after applying a magneticfield to the filter shown in FIG. 2 according to embodiments of thepresent invention;

FIG. 4 depicts a cross-sectional side view of a filter with a magneticliner according to embodiments of the present invention;

FIG. 5 depicts a cross-sectional side view of captured particles withinthe filter shown in FIG. 4 according to embodiments of the presentinvention; and

FIG. 6 depicts a cross-sectional side view of a filter according toembodiments of the present invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedescribed embodiments, the various elements illustrated in the figuresare provided with two or three digit reference numbers. With minorexceptions, the leftmost digit(s) of each reference number correspond tothe figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor device fabrication may or may not be described in detailherein. Moreover, the various tasks and process steps described hereincan be incorporated into a more comprehensive procedure or processhaving additional steps or functionality not described in detail herein.In particular, various steps in the manufacture of semiconductor devicesare well known and so, in the interest of brevity, many conventionalsteps will only be mentioned briefly herein or will be omitted entirelywithout providing the well-known process details.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, microfabrication techniques can beused to create channels of any desired dimension in a variety ofmaterials. Micro-fabricated filters enable filtration and capture ofparticles defined by the size of the channel, and removal of largerparticles. However, particles having a size less than the dimensions ofthe channel will also be captured without discrimination, or regardlessof other magnetic properties.

Another method for filtering particles in biomedical applicationsincludes attaching ligands to magnetic particles (e.g., nano-magneticparticles having nano-dimensions) coated on a surface of a substrate.Particles that preferentially attach to the ligands bound to themagnetic particles can be separated from other particles uponapplication of a magnetic field. This method captures all particles thatattach themselves preferentially to the magnetic particle, independentof their size.

Turning now to an overview of aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing a micro-machined filter that capturesparticles based on both size and magnetic properties. Microfabricationtechniques (e.g., masking, patterning, and etching) are used to createetched cavities in planar substrates. According to some embodiments ofthe present invention, the micro-machined filter is spun in a coatingchamber, and an external magnetic field is applied while a solution (orsuspension) including the magnetic particles to be filtered/captured isdispensed onto the spinning filter. By adjusting the spin accelerationand speed of the spinning substrate and the applied external magneticfield, magnetic particles can be captured within the cavities. Accordingto some embodiments of the present invention, the filter can alsoseparate nonmagnetic particles from magnetic particles by coating thecavities with a magnetic film bound to ligands that interact with themagnetic particle of interest. An external magnetic field is not neededto capture the magnetic particles, as the magnetic field from themagnetic film will bind to the magnetic particles.

The above-described aspects of the invention address the shortcomings ofthe prior art by providing a micro-machined filter that separatesmagnetic particles from nonmagnetic particles, as well as discriminatesbased on size. Applying a magnetic field to a spinning filter substrate,or coating the substrate with a magnetic material, allows the capture ofparticles based on both size and magnetic properties. According to oneor more embodiments of the invention, the filters are particularlyuseful for isolating and studying iron based clusters for example, whichplay a critical role in the chemistry and biology of many proteins.

Turning now to a more detailed description of aspects of the presentinvention, FIG. 1A depicts a top view of a filter 100 according toembodiments of the present invention. FIG. 1B depicts a cross-sectionalside view of the filter 100 according to embodiments of the presentinvention. The filter 100 includes a plurality of pores 104. Each of thepores 104 has a width (w), length (l), and depth (d) (see also FIG. 1B).The shape of the pores 104 shown is for exemplary purposes and is notintended to be limited. The shape of the pores 104 can be, for example,circular, square, rectangular, elongated, etc. The width (w) of thepores 104 is the largest spherical particle that can pass through thepore. Although the filter 100 is shown as including a first row andsecond row of pores 104, the filter 100 can include any number of rowsor numbers of pores 104.

The shape and dimensions (width (w), length (l), and depth (d)) of thepores can vary and depend on the size and type of particles to befiltered or captured. Although the pores 104 are shows as having alength (l) and depth (d) that are greater than the width (w), thedimensions of the pores 104 are not limited to these dimensions.According to some embodiments, the length (l), depth (d), and width (w)of the pores 104 are the same, or substantially the same. According toother embodiments, the shape of the pores are round holes. According toone or more embodiments of the present invention, the width (w) of thepores 104 is about 20 nm to about 5 μm. According to other embodimentsof the present invention, the width (w) of the pores 104 is about 20 nmto about 500 nm. According to one or more embodiments of the presentinvention, the length (l) of the pores 104 is about 20 nm to about 10μm. According to other embodiments of the present invention, the length(l) of the pores 104 is about 20 nm to about 1 μm. According to one ormore embodiments of the present invention, the depth (d) of the pores104 is about 40 nm to about 10 μm. According to other embodiments of thepresent invention, the depth (d) of the pores 104 is about 40 nm toabout 2 μm.

It should be noted that the pore size (width (w), depth (d), and length(l)) of the filters 100 of the present invention can be easily modifiedby photolithography, etching, and thin film deposition techniques, suchas chemical vapor deposition (CVD) of additional material on the porewalls to make the pores smaller, or thin film growth techniques such asoxidation of pore walls followed by oxide etching to make the poreslarger. The pores can also be made smaller by altering the patterning oretching processes or by growing thermal oxide on them (e.g., dryoxidation at 800° C.) which is a precisely controllable process, forsubstrates such as silicon wafers that are readily oxidized. The filters100 of the present invention can also be easily integrated with othermicro-fabricated electronic, mechanical, or electromechanical devices.The constituent materials, pore dimensions and pore shapes can also bevaried widely.

According to one or more embodiments of the present invention, thefilter 100 includes pores 104 having more than one dimension. Forexample, the filter 100 can include a plurality of regions having poresof different sizes (a plurality of widths (w), depths (d), and lengths(l)), which enables capturing particles of different sizes using thesame substrate. The filter 100 can include, for example, two or moreregions that include two or more pore sizes.

The filter is fabricated using microfabrication techniques, includingmasking, patterning, and etching, to form a micro-fabricated filter.Microfabrication includes a collection of technologies that are utilizedin making micro-devices. To fabricate a micro-device, many processesmust be performed, one after the other, many times repeatedly. Theseprocesses include, for example, depositing a film, patterning the filmwith the desired micro features, and removing (or etching) portions ofthe film. Thin film metrology is used typically during each of theseindividual process steps, to ensure the film structure has the desiredcharacteristics in terms of thickness (t), refractive index (n) andextinction coefficient (k), for suitable device behavior. The complexityof microfabrication processes can be described by their mask count. Thisis the number of different patterned layers that constitute the finaldevice.

The starting planar substrate 102 includes one or more semiconductormaterials dielectric materials, or other nonmagnetic materials.Non-limiting examples of suitable substrate materials include Si(silicon), strained Si, SiC (silicon carbide), Ge (germanium), SiGe(silicon germanium), SiGeC (silicon-germanium-carbon), Si alloys, Gealloys, III-V materials (e.g., GaAs (gallium arsenide), InAs (indiumarsenide), InP (indium phosphide), or aluminum arsenide (AlAs)), II-VImaterials (e.g., CdSe (cadmium selenide), CdS (cadmium sulfide), CdTe(cadmium telluride), ZnO (zinc oxide), ZnSe (zinc selenide), ZnS (zincsulfide), or ZnTe (zinc telluride)), or any combination thereof. Othernon-limiting examples of semiconductor materials for substrate 102include III-V materials, for example, indium phosphide (InP), galliumarsenide (GaAs), aluminum arsenide (AlAs), or any combination thereof.The III-V materials can include at least one “III element,” such asaluminum (Al), boron (B), gallium (Ga), indium (In), and at least one “Velement,” such as nitrogen (N), phosphorous (P), arsenic (As), antimony(Sb).

Non-limiting examples of dielectric materials for the substrate 102include silicon oxide, glass, a flowable oxide, a high density plasmaoxide, borophosphosilicate glass (BPSG), or any combination thereof.

Non-limiting examples of nonmagnetic materials that can be used for thesubstrate 102 include glass, quartz, plastic, or a combination thereof.

Trenches forming the pores 104 are etched in the substrate 102, forexample, by anisotropic plasma etching with a photolithography patternedmask, which is etched away after the trench etching is complete.Depending on the desired size of the pores 104, molding or stampingtechniques can be used to form the pores 104. The dimensions of thepores 104 (width (w), depth (d), and length (l)) can be adjusted usinglithography and etching techniques to optimize capture of particles of adesired size.

The pores 104 in the filter 100 do not extend all the through thesubstrate, as shown in FIG. 1B for example. Yet, in other embodiments,filters 200 (as shown in FIG. 6) includes the pores 104 that extend allthe way through the substrate 102.

There are many thin film deposition techniques that can be used todeposit the masking layer for etching the pores 104, and embodiments ofthe present invention are therefore not limited to those describedherein. Such methods include physical vapor deposition (PVD), such assputtering, e-Beam or thermal evaporation, chemical vapor deposition(CVD), plasma enhanced chemical vapor deposition (PECVD), spin-onglasses, or electro-plating. In addition, there are many etchingtechniques that can be used to form the pores 104, such as reactive ionetching (RIE), ion beam etching (IBE), and anisotropic or isotropicchemical etching.

FIG. 2 depicts a cross-sectional side view after spinning the filter 100shown in FIG. 1B according to embodiments of the present invention.After forming the filter 100 by microfabrication techniques, the filter100 is spun about an axis 206 arranged substantially perpendicular to asurface 208 (first surface or top surface) of the filter 100, accordingto one or more embodiments of the present invention. The filter 100 canbe placed inside a chamber including a surface for the filter 100. Thefilter 100 can be placed inside a coating chamber that allows the filterto spin.

The spin speed and acceleration can be adjusted and will vary dependingon the type of filter and the particles to be captured/filtered. Thespinning will cause the smaller particles, below a certain size,depending on spin speed/acceleration and particle properties, to move tothe outer edges of the substrate or even spin them right off thesubstrate. By adjusting the spin speed and acceleration the particlescan be moved that are much smaller than the desired size towards theedges or off the substrate, while trapping the particles close to thepore sizes with the pores. The particles larger than the pores will notbe trapped in the pores. According to one or more embodiments of thepresent invention, the spin speed is about 10 rpm to about 50,000 rpm insome embodiments of the present invention. The spin speed however willbe a strong function of the particle size of interest and the physicaland chemical properties of the particles. According to some embodimentsof the present invention, the spin acceleration is about 10 to about5000 rpm/s.

FIG. 3 depicts a cross-sectional side view after applying a magneticfield 303 and disposing a solution on the spinning filter 100 shown inFIG. 2 according to embodiments of the present invention. While thefilter spins 100, an external magnetic field 300 is then applied to thefilter 100 by a magnetic field generating device. The magnitude andduration of the applied external magnetic field 300, along with the spinacceleration and speed of the filter 100, are adjusted so that desiredparticles within a solution 332 are captured/filtered in the filter 100.In the presence of the magnetic field, the magnetic particles have adownward magnetic force exerted on them which forces them downward intothe pores, so that they are captured within the pores.

The widths (w) of the pores 104 are also adjusted to optimize thecapture of particles of a desired size. Therefore, a combination of theapplied magnetic field 303, the acceleration and spin speed of thefilter 100, and size of the pores 104 are used to optimize capture ofmagnetic particles having a desired dimension.

The solution 332 (or suspension) is a liquid solution that includes oneor more types of magnetic particles to be captured/filtered. The liquidsolution 332 is dispensed onto the spinning filter 100, while theexternal magnetic field 303 is being applied. First magnetic particles310 having a width (w₁) that is smaller than the width (w) of the pores104 in the filter 100 can pass through the pores 104 or pores of thefilter 100. Second magnetic particles 330 having a width (w₂) that islarger than the width (w) of the pores 104 will not pass through thepores 104 and will be separated, remaining on a surface 208 of thefilter 100. Thus, the first magnetic particles 310 of interest will becaptured within the pores. As described earlier, by adjusting the spinspeed, acceleration and strength of the magnetic field, particles withina certain size range are captured by the pores.

Various types of magnetic particles can be filtered/captured using thedescribed methods, which are applicable to a variety of biomedicalapplications. The magnetic particles (first magnetic particles 310 orsecond magnetic particles 330) can include either single particles orclusters of particles. According to one or more embodiments of thepresent invention, the magnetic particles of interest are biochemicalmetal clusters, such as iron-based clusters, that play roles in thebiochemistry of many proteins. According to some embodiments of thepresent invention, the magnetic particles include iron, nickel, cobalt,or any alloys thereof.

In addition to separating magnetic particles as described above byspinning and applying a magnetic field, the filter 100 also can be usedto separate nonmagnetic particles from desired magnetic particles. FIG.4 depicts a cross-sectional side view of the filter 100 according toembodiments of the present invention, which includes a magnetic film 406liner arranged on sidewalls of the pores 104. The magnetic film 406lines at least a portion of the pores 104 within the substrate 102. Themagnetic film 406 can be deposited by any deposition method, including,but not limited to, physical vapor deposition (PVD), chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD), orany combination thereof. The magnetic film 406 can include magneticparticles that are deposited to form a film. The magnetic film 406includes one or more magnetic materials, including, but not limited to,iron, nickel, cobalt, or alloys thereof.

The magnetic film 406 within the pores 104 can also be coated with acoating. The coating can include ligands 408 or surface functionalgroups that will bind to a desired magnetic particle, to aid in capturewithin the pores 104. The ligands 408 include any functional group orcompound that will bind to the desired magnetic particles.

FIG. 5 depicts a cross-sectional side view of magnetic particles 310captured within pores 104 of the filter 100 shown in FIG. 4 according toembodiments of the present invention. A solution 432 is dispensed ontothe filter 100. The solution 432 (or suspension) is a liquid solutionthat includes one or more types of magnetic particles to becaptured/filtered. The magnetic particles 310 will bind to ligands 408within the pores 104 of the filter 100 and are separated from thenon-magnetic particles 433. The non-magnetic particles 433 that are inthe correct size range can also fall into the pores 104, but dependingon the pore depth and the spin speed, the non-magnetic particles 433will have a higher probability of being released from the pore 104 thanthe magnetic particle, which will be held by the ligand. If thenon-magnetic particles 433, or magnetic particles, have widths that aregreater than the widths of the pores 104, then these larger particleswill remain on the surface of the filter 100. An external magnetic fieldis not needed to capture the particles of interest, since the magneticfield generated by the magnetic film 406 will hold the magneticparticles 310 of interest. Although the coating with ligands 408 aids incapturing the magnetic particles, the coating is not required, as themagnetic particles 310 can directly bind to the magnetic film 406itself.

The surface of the filters 100 of the present invention can be givenvarious chemical properties depending on the application. For example,surfaces of the filters 100 can be hydrophilic or hydrophobic. Ahydrophilic surface is useful for aqueous solutions, and a hydrophobicsurface is useful when filtering nonpolar hydrocarbons. The filters canalso be made to strongly adsorb certain types of molecules by bonding onthe surface monoclonal antibodies. The antibodies would have to bebonded at a part of the antibody that does not interfere with itsability to recognize and adsorb the desired target molecules.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The term “conformal” (e.g., a conformal layer) means that the thicknessof the layer is substantially the same on all surfaces, or that thethickness variation is less than 15% of the nominal thickness of thelayer.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown” mean the growth of a semiconductor material (crystallinematerial) on a deposition surface of another semiconductor material(crystalline material), in which the semiconductor material being grown(crystalline overlayer) has substantially the same crystallinecharacteristics as the semiconductor material of the deposition surface(seed material). In an epitaxial deposition process, the chemicalreactants provided by the source gases can be controlled and the systemparameters can be set so that the depositing atoms arrive at thedeposition surface of the semiconductor substrate with sufficient energyto move about on the surface such that the depositing atoms orientthemselves to the crystal arrangement of the atoms of the depositionsurface. An epitaxially grown semiconductor material can havesubstantially the same crystalline characteristics as the depositionsurface on which the epitaxially grown material is formed. For example,an epitaxially grown semiconductor material deposited on a {100}orientated crystalline surface can take on a {100} orientation. In someembodiments of the invention, epitaxial growth and/or depositionprocesses can be selective to forming on semiconductor surface, andcannot deposit material on exposed surfaces, such as silicon dioxide orsilicon nitride surfaces.

As previously noted herein, for the sake of brevity, conventionaltechniques related to semiconductor device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the semiconductordevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device. Semiconductor lithography is the formation ofthree-dimensional relief images or patterns on the semiconductorsubstrate for subsequent transfer of the pattern to the substrate. Insemiconductor lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures that makeup a transistor and the many wires that connect the millions oftransistors of a circuit, lithography and etch pattern transfer stepsare repeated multiple times. Each pattern being printed on the wafer isaligned to the previously formed patterns and slowly the conductors,insulators and selectively doped regions are built up to form the finaldevice.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A method for filtering magnetic particles, the method comprising: spinning a filter comprising a plurality of pores within a substrate, the pores extending from one side of the substrate but not all the way to a second side of the substrate; while spinning the filter, applying an external magnetic field to the filter; disposing a solution comprising a first particle and a second particle onto the filter, the first particle comprising a magnetic particle of interest; and separating the first particle from the second particle by capturing the first particle within a pore of the plurality of pores within the substrate.
 2. The method of claim 1, wherein the substrate comprises a semiconductor material, a dielectric material, a non-magnetic material, or a combination thereof.
 3. The method of claim 2, wherein the semiconductor material comprises silicon.
 4. The method of claim 2, wherein the dielectric material comprises glass.
 5. The method of claim 1, wherein the spinning of the filter comprises spinning the filter about an axis perpendicular to a surface of the substrate.
 6. The method of claim 1, wherein the first particle has a width that is less than a width of each pore of the plurality of pores within the substrate.
 7. The method of claim 6, wherein the second particle has a width that is greater than the width of each pore of the plurality of pores within the substrate. 